the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
DQPB: software for calculating disequilibrium U-Pb ages
Timothy John Pollard
Jon David Woodhead
John Charles Hellstrom
John Engel
Roger Powell
Russell Neil Drysdale
Abstract. DQPB is software for calculating U-Pb ages while accounting for the effects of radioactive disequilibrium among intermediate nuclides of the U-series decay chains. The software is written in Python and distributed both as a pure Python package, and a stand-alone GUI application that integrates with standard Microsoft Excel spreadsheets. The software implements disequilibrium U-Pb equations to compute ages using various approaches, including concordia-intercept ages on a Tera-Wasserburg diagram, disequilibrium U-Pb isochron ages, Pb/U ages based on single analyses, and modified 207Pb ages. These age calculation approaches are tailored toward young materials that cannot reasonably be assumed to have attained radioactive equilibrium at the time of analysis, although they may also be applied to older materials where disequilibrium is no longer analytically resolvable. The software allows users to implement a variety of regression algorithms using both classical and robust statistics approaches, compute weighted average ages, and construct customisable, publication-ready plots of U-Pb age data. Age uncertainties are propagated using Monte Carlo methods.
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Timothy John Pollard et al.
Status: closed
-
RC1: 'Comment on gchron-2022-24', Pieter Vermeesch, 31 Oct 2022
- AC2: 'Reply to RC1', Timothy Pollard, 08 Dec 2022
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RC2: 'Comment on gchron-2022-24', Ryan Ickert, 10 Nov 2022
Review of “DQPB: software for calculating disequilibrium U-Pb ages” by Pollard et al., submitted to Geochronology.
This review is by Ryan Ickert (Purdue University)
This manuscript briefly describes the functioning of a software package designed primarily to reduce U-Pb data from speleothems derived by ICP-MS, where the samples are young enough to require corrections for intermediate daughter products disequilibrium. Overall, this is an excellent manuscript and is suitable for publication in Geochronology. I was fortunate to be able to read the excellent comment by Pieter Vermeesch prior to writing this review. I won’t repeat what he said, but I very much endorse his recommendation regarding the treatment of 234U. The manuscript is written in a very clear and concise manner, the equations are suitable and written in a way that makes them relatively easy to follow, the examples are well-chosen, and the figures are well-drafted. The references are particularly well chosen to isolate both early literature, significant work from the 80s and 90s, and appropriate works that highlight recent developments. Having done a deep dive into some of this literature myself a few years ago, I appreciate the well-curated references.
Regarding the software itself, I think that the authors have struck a good balance between accessibility and availability to more programming-savvy users. I applaud the use of Github and the use of a specific license allowing modification.
The following are some minor points, some of which the authors might consider in a revised manuscript. I appreciate that generally authors are encouraged to respond to these reviews, but I don’t see any reason that they should necessarily do so in this case. I encourage them instead to engage fully with the Vermeesch review.
Line 30: The statement about zircon excluding Th implies to me that Th is incompatible in zircon (e.g., the mineral/melt partition coefficient is less than 1). This is not correct. Thorium is typically compatible in zircon, but simply less compatible than uranium, which leads to a deficit in 230Th relative to 238U, though an *overall* increase relative to a melt.Line 62: The password is “armpit”.
Line 164: It might be useful to a reader, at this point, to guide them towards Schmitt (2007, American Mineralogist V92 p691-694) where Pa/U partitioning in zircon was directly constrained. The rest of this manuscript is so comprehensive it would probably fit in nicely.
Figure 4: The figure is not present in my copy of the manuscript, but I assume this is a typesetting error.Line 287: This is an incredibly trivial point but I think that “adopted” is probably overstating the degree to which robust statistics have been used in geochronology. The vast majority of data is treated with classical statistics – I would think that “proposed for” rather than “adopted in” is appropriate.
Citation: https://doi.org/10.5194/gchron-2022-24-RC2 -
AC1: 'Reply to RC2', Timothy Pollard, 08 Dec 2022
We thank Ryan Ickert for his positive comments regarding the manuscript presentation and other helpful suggestions. We address his specific comments below.
Comment: ‘The statement about zircon excluding Th implies to me that Th is incompatible in zircon (e.g., the mineral/melt partition coefficient is less than 1). This is not correct. Thorium is typically compatible in zircon, but simply less compatible than uranium, which leads to a deficit in 230Th relative to 238U, though an *overall* increase relative to a melt.’
Response: We have made the language here more explicit in the revised manuscript.
Comment: The password is “armpit”.
Response: Regarding the ‘protected’ nature of the Isoplot software, we believe there are two issues here. One is indeed the fact that the VBA source code for most versions of Isoplot is password protected, although this password protection seems to have been lifted from the most recent versions. A second, and more important issue, is that the licensing status of Isoplot is ambiguous. It seems that Isoplot can be downloaded by anyone free of charge and used without restriction, but it is not clear that modification and re-distribution of the source code is permissible. We have modified the sentence here to spell this point out more explicitly.
Comment: Line 164: It might be useful to a reader, at this point, to guide them towards Schmitt (2007, American Mineralogist V92 p691-694) where Pa/U partitioning in zircon was directly constrained.
Response: We appreciate the suggestion and have included a reference to this work in the revised manuscript.
Comment: Figure 4: The figure is not present in my copy of the manuscript, but I assume this is a typesetting error.
Response: Unfortunately, this image file was corrupted and does not render properly in certain pdf software (Adobe software being one example). We were made aware of this by the editorial support team after initial submission but were not provided with an opportunity to substitute a new file.
Comment: This is an incredibly trivial point but I think that “adopted” is probably overstating the degree to which robust statistics have been used in geochronology. The vast majority of data is treated with classical statistics – I would think that “proposed for” rather than “adopted in” is appropriate.
Response: This is a fair point and we have adjusted the sentence accordingly.
Citation: https://doi.org/10.5194/gchron-2022-24-AC1
-
AC1: 'Reply to RC2', Timothy Pollard, 08 Dec 2022
Status: closed
-
RC1: 'Comment on gchron-2022-24', Pieter Vermeesch, 31 Oct 2022
- AC2: 'Reply to RC1', Timothy Pollard, 08 Dec 2022
-
RC2: 'Comment on gchron-2022-24', Ryan Ickert, 10 Nov 2022
Review of “DQPB: software for calculating disequilibrium U-Pb ages” by Pollard et al., submitted to Geochronology.
This review is by Ryan Ickert (Purdue University)
This manuscript briefly describes the functioning of a software package designed primarily to reduce U-Pb data from speleothems derived by ICP-MS, where the samples are young enough to require corrections for intermediate daughter products disequilibrium. Overall, this is an excellent manuscript and is suitable for publication in Geochronology. I was fortunate to be able to read the excellent comment by Pieter Vermeesch prior to writing this review. I won’t repeat what he said, but I very much endorse his recommendation regarding the treatment of 234U. The manuscript is written in a very clear and concise manner, the equations are suitable and written in a way that makes them relatively easy to follow, the examples are well-chosen, and the figures are well-drafted. The references are particularly well chosen to isolate both early literature, significant work from the 80s and 90s, and appropriate works that highlight recent developments. Having done a deep dive into some of this literature myself a few years ago, I appreciate the well-curated references.
Regarding the software itself, I think that the authors have struck a good balance between accessibility and availability to more programming-savvy users. I applaud the use of Github and the use of a specific license allowing modification.
The following are some minor points, some of which the authors might consider in a revised manuscript. I appreciate that generally authors are encouraged to respond to these reviews, but I don’t see any reason that they should necessarily do so in this case. I encourage them instead to engage fully with the Vermeesch review.
Line 30: The statement about zircon excluding Th implies to me that Th is incompatible in zircon (e.g., the mineral/melt partition coefficient is less than 1). This is not correct. Thorium is typically compatible in zircon, but simply less compatible than uranium, which leads to a deficit in 230Th relative to 238U, though an *overall* increase relative to a melt.Line 62: The password is “armpit”.
Line 164: It might be useful to a reader, at this point, to guide them towards Schmitt (2007, American Mineralogist V92 p691-694) where Pa/U partitioning in zircon was directly constrained. The rest of this manuscript is so comprehensive it would probably fit in nicely.
Figure 4: The figure is not present in my copy of the manuscript, but I assume this is a typesetting error.Line 287: This is an incredibly trivial point but I think that “adopted” is probably overstating the degree to which robust statistics have been used in geochronology. The vast majority of data is treated with classical statistics – I would think that “proposed for” rather than “adopted in” is appropriate.
Citation: https://doi.org/10.5194/gchron-2022-24-RC2 -
AC1: 'Reply to RC2', Timothy Pollard, 08 Dec 2022
We thank Ryan Ickert for his positive comments regarding the manuscript presentation and other helpful suggestions. We address his specific comments below.
Comment: ‘The statement about zircon excluding Th implies to me that Th is incompatible in zircon (e.g., the mineral/melt partition coefficient is less than 1). This is not correct. Thorium is typically compatible in zircon, but simply less compatible than uranium, which leads to a deficit in 230Th relative to 238U, though an *overall* increase relative to a melt.’
Response: We have made the language here more explicit in the revised manuscript.
Comment: The password is “armpit”.
Response: Regarding the ‘protected’ nature of the Isoplot software, we believe there are two issues here. One is indeed the fact that the VBA source code for most versions of Isoplot is password protected, although this password protection seems to have been lifted from the most recent versions. A second, and more important issue, is that the licensing status of Isoplot is ambiguous. It seems that Isoplot can be downloaded by anyone free of charge and used without restriction, but it is not clear that modification and re-distribution of the source code is permissible. We have modified the sentence here to spell this point out more explicitly.
Comment: Line 164: It might be useful to a reader, at this point, to guide them towards Schmitt (2007, American Mineralogist V92 p691-694) where Pa/U partitioning in zircon was directly constrained.
Response: We appreciate the suggestion and have included a reference to this work in the revised manuscript.
Comment: Figure 4: The figure is not present in my copy of the manuscript, but I assume this is a typesetting error.
Response: Unfortunately, this image file was corrupted and does not render properly in certain pdf software (Adobe software being one example). We were made aware of this by the editorial support team after initial submission but were not provided with an opportunity to substitute a new file.
Comment: This is an incredibly trivial point but I think that “adopted” is probably overstating the degree to which robust statistics have been used in geochronology. The vast majority of data is treated with classical statistics – I would think that “proposed for” rather than “adopted in” is appropriate.
Response: This is a fair point and we have adjusted the sentence accordingly.
Citation: https://doi.org/10.5194/gchron-2022-24-AC1
-
AC1: 'Reply to RC2', Timothy Pollard, 08 Dec 2022
Timothy John Pollard et al.
Data sets
Sambe-Kisuki tephra LA-ICP-MS zircon example U-Pb data set Shuhei Sakata (unpublished) https://github.com/timpol/DQPB/blob/main/tests/datasets/SambeZircon.csv
CCB6 stalagmite example U-Pb data set Timothy Pollard, Jon Woodhear, John Hellstrom and Russell Drysdale (unpublished) https://github.com/timpol/DQPB/blob/main/tests/datasets/CCB6.csv
Timothy John Pollard et al.
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